This invention relates to a method for manufacturing a conductive thin film patterned substrate or a substrate having a conductive thin film patterned thereon, and more particularly to a method for a patterning a conductive thin film such as a transparent conductive thin film of ITO, SnSbO, ZnAlO or the like or a metal thin film of Al or the like by thick film printing.
Conventionally, in manufacturing of, for example, a fluorescent display device for graphic display, a transparent conductive film of indium tin oxide (ITO) or the like or a metal film of Al or the like is formed on a surface of a glass substrate and then a photoresist is coated on the conductive thin film laminatedly or by lamination. Then, the thus-coated photoresist is subject to photolithography wherein exposure, development and etching are carried out with respect to the photoresist, so that conductive thin film patterns may be provided on the substrate.
Then, an insulating layer is formed in each of gaps between the thus-formed conductive thin film patterns by thick film printing or the like. Subsequently, a phosphor layer is formed on each of display regions of the conductive thin film by electro-deposition, thick film printing or the like, to thereby provide anode electrodes.
Unfortunately, the conventional techniques described above cause the number of steps carried out for patterning of the conductive thin film made of ITO, SnSbO, ZnAlO or Al in photolithography to be increased. In addition, the conventional techniques require a troublesome after-treatment such as a treatment of waste liquid produced in washing and etching steps.
There has been also known in the art a powdery etching material which can be printed on a surface of a glass substrate and then subject to calcination and washing with water for removal from the glass substrate. In addition, there has been developed a paste material which can be used for screen printing and decomposed by calcination to provide an ITO film. However, such materials each fail to exhibit conductivity equal to that of a film formed by sputtering.
Furthermore, there has been provided a thin film in the prior art which is made of SnSbO and known as a nesa film in the art. The thin film is increased in chemical strength, resulting in being promising as a transparent conductive film such as that for a display device. However, it has a problem of rendering formation of patterns difficult.
The present invention has been made in view of the foregoing disadvantage of the prior art.
Research and development by the inventors on a fluorescent display device revealed that when a paste of phosphate fritted glass which is used as a sealing agent during formation of an envelope for a fluorescent display device is deposited in the form of a film on an ITO conductive thin film and then subject to calcination, the ITO film arranged under the phosphate glass loses conductivity.
As a result of our careful study of the above-described phenomenon, it was found that the SnOxe2x80x94P2O5xe2x80x94ZnO glass or phosphate low-melting glass which is deposited laminatedly or by lamination on a surface of the ITO conductive thin film formed on a surface of an insulating substrate has a softening point of 425xc2x0 C., therefore, calcination of the glass at 500xc2x0 C. in an air atmosphere leads to a reduction in viscosity of the glass, resulting in InO2 and SnO2 which permit the ITO film to exhibit conductivity melting into the glass at an interface between the ITO film and the glass, to thereby cause vanishment of the ITO and therefore vanishment of InO2 and SnO2. This would be the reason why the conductivity is lost.
This was proved by the fact that microscopic observation which was made on a region or portion of the ITO positioned below the phosphate glass which lost conductivity clearly revealed melting of the ITO film into the glass softened, as described hereinafter with reference to FIGS. 1 to 3.
Further, a fluorescent display device was manufactured by laminatedly depositing an insulating paste mainly consisting of the above-described SnOxe2x80x94P2O5xe2x80x94ZnO glass which is phosphate glass on an ITO film formed on a glass substrate and then subjecting the glass substrate to calcination at 500xc2x0 C. in an air atmosphere to form an insulating layer, followed by lamination of a phosphor layer on each of conductive regions or portions of the ITO film. As a result, it was found that arrangement of the insulating layer permits a resistance of electrodes adjacent thereto to be increased to a level as high as 2 to 5Mxcexa9 or more. This indicates that the fluorescent display device exhibits satisfactory insulating properties.
Accordingly, it is an object of the present invention to provide a method for manufacturing a conductive thin film patterned substrate which is capable of being practiced at a reduced cost without substantially causing any environmental pollution.
It is another object of the present invention to provide a method for manufacturing a conductive thin film patterned substrate which is capable of eliminating any troublesome after-treatment as required in the prior art.
In accordance with the present invention, a method for manufacturing a conductive thin film patterned substrate is provided. The method includes the steps of forming a conductive thin film on an insulating substrate and carrying out pattern formation of an insulating thick film layer consisting of low-softening glass having a chemical composition which leads to vitrification of the conductive thin film formed on the insulating substrate. The insulating thick film layer is formed on the conductive thin film. The method also includes the step of carrying out calcination which permits a portion of the conductive thin film positioned under the insulating thick film layer to be vitrified integrally with the insulating thick film layer.
Also, in accordance with the present invention, a method for manufacturing a conductive thin film patterned substrate is provided. The method includes the steps of forming a conductive thin film on an insulating substrate and printing a paste consisting of a low-softening glass powder having a chemical composition which leads to vitrification of the conductive thin film on portions of the conductive thin film which are desired to be changed so as to exhibit insulating properties, to thereby carry out pattern formation of an insulating thick film layer. The insulating thick film layer is formed on the conductive thin film. The method also includes the step of carrying out calcination which permits a portion of the conductive thin film layer positioned under the insulating thick film layer to be vitrified integrally with the insulating thick film layer, whereby patterning of an insulating thin film region and a conductive thin film region is carried out.
In a preferred embodiment of the present invention, the conductive thin film has a thickness of 300 nm or less.
In a preferred embodiment of the present invention, the conductive thin film is made of a material selected from the group consisting of materials represented by general formulas InSnO, SnSbO and ZnAlO, and Al.
In a preferred embodiment of the present invention, the low-softening glass is phosphate glass.
In a preferred embodiment of the present invention, the low-softening glass is SnOxe2x80x94P2O5xe2x80x94ZnO glass.